THE CHESTER AMPHIBOLITE AND SERPENTINES. 113 



in IMiddletield, and probably found in the valley of the Westfield in the 

 north part of Russell. 



IS. "Black serpentine, talc, actinolifc. — Westfield." XIII, No. 24, 

 Massachusetts Survey Collection. Subgranular, dull black, very little talc, 

 derived from enstatite. 



The actinolite mentioned above is in part enstatite partially changed 

 to bastite, in part fine radiating tufts of tremolite, green from the back- 

 ground of serpentine. The rock is traversed by veins of snow-white, 

 fibrous calcite 20-30'"'" long and 2°"" wide, with satiny transverse fibers 

 and central suture. 



It shows under the microscope large masses of unchanged pyroxene 

 with coarse oo P cleavage, and long, black microlites, often crossing each 

 other rectangularly in three directions. It changes outwardly into coarse, 

 radiated, fibrous tremolite (cleavage 124°), which is altered along prismatic 

 and transverse cleavage into serpentine. 



19. "Serpentine and calcite. — Westfield." XIII, Nos. 27, 28, 29, 30, 

 Massachusetts Survey Collection. The first two are wanting in the collec- 

 tion. No. 29 is a contact piece of dolomite, with light-green and straw- 

 colored serpentine running out into it from a mass of oil-green serpentine 

 with fine, broad veins of chrysotile and many characteristic eozoonal struc- 

 tures. It shows beautifully every stage of the change of dolomite into a 

 colorless, almost perfectly amorphous serpentine, showing no needles and 

 only faint patches of color with crossed nicols, and in many cases these 

 serpentine gi-ains retain perfectly the cleavage and the repeated twinning 

 planes of the dolomite. 



No. 30 is a white, bedded limestone with distant, thin partings of ser- 

 pentine, probably originally an actinolitic limestone. Traces of hornblende 

 with extinction 14° could be seen. 



20. "Massive garnet.— Westfield." XIII, No. 40, Massachusetts Survey 

 Collection. — This is a granular mixture of quartz, garnet, and pyroxene, and 

 can have been introduced here only as one of the rocks bordering upon 

 the Atwater serpentine bed. 



31. " Compact scapolite (?).— Westfield." XIII, No. 32, Massachusetts 

 Survey Collection.— A bluish-white, translucent, partly sparry, partly cryp- 

 tocrystalline mass, showing the distinct, very fine, triclinic striation of a 

 plagioclase, exactly like that associated with the serpentine at the Chester 

 emery mine and at the Pelham asbestos quarry. 



MON XXIX 8 



